Histopathology: healing

Transcription

1 Histopathology: healing These presentations are to help you identify, and to test yourself on identifying, basic histopathological features. They do not contain the additional factual information that you need to learn about these topics, or necessarily all the images from resource sessions. This presentation contains images of basic histopathological features of organization and healing, including bone, with examples of situations in which it occurs. Before viewing this presentation you are advised to review relevant histology, relevant sections on healing in a pathology textbook, relevant lecture notes and relevant sections of a histopathology atlas. Copyright University of Adelaide 2011 (The histopathology of healing, including fracture healing, is introduced in semester 2 year 1)

2 Healing involves regeneration of cells (depending on cell type - labile, stable, permanent) and/or the formation of scar tissue. Depending on the extent of damage and the tissue involved, there may be a combination of both e.g. in skin wounds the epidermis can regenerate but scarring will occur in the dermis, or just scarring e.g. following myocardial infarction. Scar tissue is generally formed by an intermediary tissue called granulation tissue. The process of scar tissue formation is called organization. Wounds with closely opposed edges e.g. sutured wounds take less time to heal (healing by primary intention) than wounds/injuries in which large areas of damaged tissue need to be replaced by scar tissue (e.g. myocardial and renal infarcts, peptic ulcers, large burns). Organization follows an acute inflammatory response following tissue damage but is also a component of chronic inflammatory responses where there is ongoing tissue damage.

3 Granulation tissue. The components of granulation tissue include macrophages (black arrows), fibroblasts and myofibroblasts (yellow arrows), newly formed capillaries (blue arrows) and lymphocytes (red arrows). Following an acute inflammatory response, myofibroblasts and endothelial cells start to migrate into the area of injury about 3 days after the injury but it will take some days for granulation tissue to form and be readily seen. Early granulation tissue may be somewhat oedematous. This section is from a healing myocardial infarction. Residual myocardial cells are seen top left.

6 M Very low power view of a chronic peptic ulcer of the stomach. This one only penetrates into submucosa. Chronic peptic ulcers display a combination of ongoing acute inflammation, chronic inflammation and healing. There is ongoing necrosis and acute inflammation in response to acid in the gastric lumen, but chronic inflammation and scarring occur in the surrounding wall in an attempt at healing. There are classically several layers in the base of a chronic peptic ulcer (detail difficult to appreciate here) a) necrotic slough and acute inflammatory exudate (yellow star) b) granulation tissue (red star) c) scar tissue (blue stars) Patchy aggregates of lymphocytes (black arrows), seen as dark areas/dark dots due to their high N:C ratio on this low power, are also noted around the ulcer. Make sure you can identify the layers of the wall. M: mucosa SM: submucosa MP: muscularis propria S: serosa Ulcer crater MP SM S SM MP

7 Thrombi heal by organization. The image is of a coronary artery. An occlusive thrombus in the lumen has been replaced with loose connective tissue (black star). There is recanalization (formation of new blood vessels through the blocked lumen e.g. black arrows) but the vessels are small and will not carry sufficient blood through the blockage to supply distal tissues. Residual fibrous atherosclerotic plaque is also noted (yellow stars).

8 Granulation tissue at the base of a skin ulcer. Note newly formed blood vessels (e.g. black arrows), myofibroblasts (e.g. yellow arrows) and inflammatory cells (nuclei represented by dark dots), here a combination of both neutrophils and lymphocytes though the distinction is not apparent at this fairly low power.

9 Normal Infarcted Infarcted Normal No macroscopic or histopathologic changes are seen for 6-8 hours following infarction. In infarcts of solid tissues the necrosis is of coagulative type, which is characterised by retention of cellular and architectural outlines and also increased eosinophilic staining of infarcted cells compared to viable cells due to coagulated proteins. The nuclei fade (karyolysis) and eventually disappear from the cells (seen on higher power view at top) of this early myocardial infarction (12-24 hours). The changes are best seen when infarcted tissue is compared with adjacent viable/normal tissue.

10 Viable cells Myocardial infarction (12-24 hours). Neutrophils (e.g. black arrows) start to infiltrate the dead myocardium as part of an acute inflammatory response to tissue injury. Most of the myocardial cells in this field are dead, indicated by their increased eosinophilic staining and lack of nuclei (compare with the few viable cells still present). Contraction bands can be seen (yellow arrows) in the dead myocytes.

12 Healing myocardial infarction (one - several weeks). Myofibroblasts and endothelial cells start to migrate into the area of injury about 3 days after the injury but it will take some days for granulation tissue to be readily seen. Vascular granulation tissue predominantly comprises macrophages, myofibroblasts and fibroblasts, newly formed capillaries and lymphocytes. As time progresses, more and more connective tissue is deposited. Necrotic muscle is present on the right.

13 Scar tissue (high power) in healed myocardial infarction. With time the fibroblasts lay down more connective tissue, inflammatory cells drain via lymphatics and capillaries degenerate leaving mature scar that takes 6-8 weeks to form. There is a collagen rich extracellular matrix with a few residual fibroblasts (e.g. yellow arrows) and capillaries (yellow star). A few viable myocardial cells (black stars) are present at the edge of the scar.

14 External callus Cortical bone Medullary cavity Healing of a fracture (here from a rabbit, very low power) occurs by the formation of callus. This develops gradually following initial haemorrhage and acute inflammation. Osteoprogenitor cells migrate from the periosteum into and around the fracture site and form new unmineralised bone i.e. osteoid (the eosinophilic trabeculae seen here around the outside of the bone forming the external callus) and in some cases cartilage (black arrows). Osteoclasts remove dead bone. The callus here is well developed. Gradually, mature bone forms in the fracture gap reconstituting the dense cortical bone, and the no longer needed callus is gradually removed. Remodelling and strengthening can continue for months.

15 Cortical bone Cartilage Callus Callus may include cartilage. Cartilage matrix generally appears blue or purple due to the acidic nature of components of the matrix.

21 Photomicrograph of the surface of a rib near a fracture that has been healing for 5 days (rabbit). Osteogenic cells have differentiated into osteoblasts that have formed bony trabeculae cemented to the bone. This region is vascular. Toward the right, the osteogenic cells have differentiated into chondroblasts that have formed a mass of avascular cartilage. (from Ham s Histology, 9th edition. D.H. ormack, J.B. Lippincott Company)

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